A typical spectrometer includes a plurality of detector elements. When the spectrometer is illuminated with radiation having multiple wavelengths, each detector element records an intensity factor for a particular wavelength. The wavelength assignment of each detector element should be the value of the particular wavelength that reaches that detector after passing through the spectrometer optics. In order to determine the wavelength assignment of each detector element, the spectrometer is calibrated using a source that emits radiation at a few known wavelength points in the spectrum. The spectrometer receives the radiation and records an intensity value for the known wavelength points. In order to determine the wavelength assigned to each detector element, a functional fit or polynomial fit is performed to interpolate points within the spectrum and extrapolate points outside the spectrum. However, the wavelength assignments obtained by this method of calibration are typically accurate only to approximately one nanometer.